In a high-voltage DC converter valve, performance of a thyristor trigger unit is of utmost importance. In some DC projects, an exposed TE plate is directly installed in a converter valve. Although the installation is convenient and space-saving is achieved with this approach, the stain-resistant and anti-interference capabilities are relatively poor, and a fault may occur after prolonged operation.
Other thyristor trigger units for the converter valve may be installed in the following manner: A main trigger circuit board is packaged in a shell, and then, the shell is screw-fixed on a radiator at a valve layer. A detachable panel of the trigger unit is located at a bottom part of the shell, and the main circuit board is fixed on an inner side face of the shell. The following problems are found during implementation.
First, when the main trigger circuit board is being fixed inside the shell, because the shell body is relatively flat and anchor screws are located on a side of the shell, it is difficult to reach into the shell with a hand to align anchor points on the circuit board with those on the shell.
Second, during commissioning, when it is required to use an oscilloscope to measure an onboard signal, it is difficult to extend a probe from a relatively narrow bottom face into the shell to perform measurement.
The thyristor trigger unit used in an ice-melting project is also of a flat cuboid structure. It comprises a bottom retaining plate and an upper housing. A main circuit board is installed on the rectangular retaining plate, and the cuboid upper housing covers the main circuit board. Several holes are formed on the upper housing for passage of optical fibers and cables. The trigger unit is fixed via a small portion extending from the bottom retaining plate.
Such a shell structure of the thyristor trigger unit facilitates installation and fixation of the circuit board inside the shell, but has some disadvantages:
First, because the bottom retaining plate is relatively broad, and the extension is also relatively broad, a large installation and fixing space is required, and the shell is not applicable when a relatively narrow radiator is used in a relatively compact valve.
Second, because optical fibers and cables go through the holes on the upper housing, when the upper housing needs to be removed during commissioning of the thyristor trigger unit, the optical fibers and the cables need to be disconnected as well, and as a result need to be reconnected after the commissioning, bringing about great troubles to the commissioning.